fix(material/core): add fallback if ripples get stuck

Currently ripples assume that after the transition is started, either a `transitionend` or `transitioncancel` event will occur. That doesn't seem to be the case in some browser/OS combinations and when there's a high load on the browser.

These changes add a fallback timer that will clear the ripples if they get stuck.

Fixes angular#29159.

src/material/core/ripple/ripple-renderer.ts

@@ -28,6 +28,7 @@ export interface RippleTarget {
 interface RippleEventListeners {
   onTransitionEnd: EventListener;
   onTransitionCancel: EventListener;
+  fallbackTimer: ReturnType<typeof setTimeout> | null;
 }
 
 /**
@@ -193,14 +194,31 @@ export class RippleRenderer implements EventListenerObject {
     // are set to zero. The events won't fire anyway and we can save resources here.
     if (!animationForciblyDisabledThroughCss && (enterDuration || animationConfig.exitDuration)) {
       this._ngZone.runOutsideAngular(() => {
-        const onTransitionEnd = () => this._finishRippleTransition(rippleRef);
+        const onTransitionEnd = () => {
+          // Clear the fallback timer since the transition fired correctly.
+          if (eventListeners) {
+            eventListeners.fallbackTimer = null;
+          }
+          clearTimeout(fallbackTimer);
+          this._finishRippleTransition(rippleRef);
+        };
         const onTransitionCancel = () => this._destroyRipple(rippleRef);
+
+        // In some cases where there's a higher load on the browser, it can choose not to dispatch
+        // neither `transitionend` nor `transitioncancel` (see b/227356674). This timer serves as a
+        // fallback for such cases so that the ripple doesn't become stuck. We add a 100ms buffer
+        // because timers aren't precise. Note that another approach can be to transition the ripple
+        // to the `VISIBLE` state immediately above and to `FADING_IN` afterwards inside
+        // `transitionstart`. We go with the timer because it's one less event listener and
+        // it's less likely to break existing tests.
+        const fallbackTimer = setTimeout(onTransitionCancel, enterDuration + 100);
+
         ripple.addEventListener('transitionend', onTransitionEnd);
         // If the transition is cancelled (e.g. due to DOM removal), we destroy the ripple
         // directly as otherwise we would keep it part of the ripple container forever.
         // https://www.w3.org/TR/css-transitions-1/#:~:text=no%20longer%20in%20the%20document.
         ripple.addEventListener('transitioncancel', onTransitionCancel);
-        eventListeners = {onTransitionEnd, onTransitionCancel};
+        eventListeners = {onTransitionEnd, onTransitionCancel, fallbackTimer};
       });
     }
 
@@ -352,6 +370,9 @@ export class RippleRenderer implements EventListenerObject {
     if (eventListeners !== null) {
       rippleRef.element.removeEventListener('transitionend', eventListeners.onTransitionEnd);
       rippleRef.element.removeEventListener('transitioncancel', eventListeners.onTransitionCancel);
+      if (eventListeners.fallbackTimer !== null) {
+        clearTimeout(eventListeners.fallbackTimer);
+      }
     }
     rippleRef.element.remove();
   }

src/material/slider/slider.spec.ts

@@ -691,8 +691,8 @@ describe('MDC-based MatSlider', () => {
     it('should show the active ripple on pointerdown', fakeAsync(() => {
       expect(isRippleVisible('active')).toBeFalse();
       pointerdown();
-      flush();
       expect(isRippleVisible('active')).toBeTrue();
+      flush();
     }));
 
     it('should hide the active ripple on pointerup', fakeAsync(() => {
@@ -1831,7 +1831,7 @@ function setValueByClick(
   input.focus();
   dispatchPointerEvent(inputElement, 'pointerup', x, y);
   dispatchEvent(input._hostElement, new Event('change'));
-  tick();
+  flush();
 }
 
 /** Slides the MatSlider's thumb to the given value. */